Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing – Routing data updating
Reexamination Certificate
1998-10-13
2002-09-24
Winder, Patrice (Department: 2155)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
Routing data updating
Reexamination Certificate
active
06457059
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a communication control unit for controlling aport to be used, for example, when a packet is transferred by using a multicast-supporting LAN (Local Area Network) as well as to a communication control method applied for a multicast-supporting LAN.
BACKGROUND OF THE INVENTION
In association with rapid and widespread use of personal computers in recent years, LAN has also become increasingly common, while computers and networks themselves have been more advanced and more powerful. In addition, wide use of WWW (World Wide Web) as well as of multimedia data such as moving images and voice is progressing, and the traffic of networks is more and more increasing, so that introduction of network repeater such as a communication control unit and a high speed router, for example, a switching hub allowing large amounts of data to be transmitted with high speed to a network is progressing. Further, data transfer based on a multicast technology has been started as a technology for efficiently transferring large amounts of data, and it may be estimated that the widespread use of data transfer using a multicast is more and more increasing from now on.
Description is made hereinafter for a multicast-supporting LAN in which a conventional type of communication control unit is applied.
FIG. 15
is a view showing a construction of the conventional type of multicast-supporting LAN. The multicast-supporting LAN shown in
FIG. 15
comprises multicast routers
1001
and
1002
for relaying data transfer using a multicast according to an IP address; communications control units
1101
,
1102
, and
1103
for switching input/output of a packet with data to be transferred according to MAC addresses; a hub
1201
functioning as, for example, a multi-port transceiver; and host devices
1301
-
1307
each functioning as a terminal. The network construction shown in
FIG. 15
is a part of a LAN taken out to describe the network based on the conventional technology.
FIG.
16
and
FIG. 17
are views for explaining a general outline of an operation of IGMPv2 (Internet Group Management Protocol Version 2),
FIG. 16
shows a sequence for a host device to become a member of a multicast group, and
FIG. 17
shows a sequence for a host device to leave a multicast group. It should be noted that FIG.
16
and
FIG. 17
show a construction obtained by taking out a part with the multicast router
1001
and host devices
1304
and
1305
from the construction in FIG.
15
.
At first, description is made for a method of becoming a member of a multicast group with reference to FIG.
16
. It is assumed here that the host device
1305
desires a member of a multicast group, and description is made for the operation within a range of the construction shown in
FIG. 16
to make description simpler. The multicast router
1001
periodically transmits a query message (Host Membership Query) to a destination with the IP address 224.0.0.1 (All-Systems-Group) to ask the host devices
1304
and
1305
each connected to a local network to become a member of one of multicast groups and to find out where the desired multicast group exists.
In this case, the host device
1305
having a desire of becoming a member of a multicast group transmits a report message (Host Member Report) to a multicast address of a group hoping to become a member to report the multicast address of which the host device desires a member in response to the received a query from the multicast router
1001
.
At this point of time, the host device
1305
trying to transmit a report transmits the report at a random time during a period of time until a Max Response Time (Default: 10 sec) included in the query message is elapsed. If there are a plurality of other host devices each to send a report to the same group as that the report to be sent to, the multicast router receives a first transmitted report by one of host devices, so that the other host devices do not transmit the report. Namely, when a plurality of host devices in a network medium are connected to shared media, only one report for each multicast group is transmitted.
The multicast-supporting router
1001
receives the report, finds out a multicast group of which the host device
1305
desires a member, and starts to transmit, if it is found where a multicast for the multicast group exists, multicast data to a local network based on a multicast routing protocol.
Next description is made as to a method of leaving a multicast group with reference with FIG.
17
. It is assumed here that the host device
1305
desires to leave a multicast group, and description is made for the operation within a range of the construction shown in
FIG. 17
to make description simpler. The host device
1305
desiring to leave the multicast group of which the device is a member transmits a leave message to the IP address 224.0.0.2 (All-Routers-Group) at the point of time when leaving is decided.
The multicast router
1001
having received the leave transmits a GS query (Group Specific Query) message to the multicast group address to check whether any other host devices each being a member of the multicast group exist or not. If there are some host devices each as a member of the multicast group other than the host device having transmitted the leave, the host device
1305
transmits a report to the multicast router
1001
to convey the existence thereof.
Herein, although there is also Version 1 of IGMP (defined in RFC1112), IGMPv2 supports compatibility with IGMPv1, so that any host device and router supporting Version 1 may exist in a local network. Leave is a message added in IGMPv2, namely, in Version 1, a multicast router finds out existence or leaving of a receiving host device depending on presence or absence of a response with a report to periodical transmission of a query.
Conventionally, unicast physical addresses of terminals each connected to each port are stored in a communication control unit such as a switching hub, and high speed packet transfer of a unicast packet having a unicast physical address of a terminal or of a broadcast packet to terminals is realized only to a target port or target ports based on a hardware switching technology.
As for a multicast packet used for multimedia data transfer, however, it is difficult to discriminate a plurality of particular ports requiring the multicast packet from others as compared to the case of unicast, and for this reason, a multicast packet is not transferred only to ports requiring the multicast packet but is transferred to all ports like the broadcast packet.
The multicast packet as described above has in many cases continuous stream data as well as a large amount of data with a data type of moving images and other data, which causes limitations of processing by the communication control unit, and for this reason, there occur inconveniences such that a disposal rate of multicast packets becomes higher, a transfer delay time becomes longer, or a bad influence is given to transfer of other unicast packet.
Although there is a device for performing message transaction with a multicast router connected to a network using a particular protocol to transfer a multicast packet only to a port of a required communication control unit, the operation of transferring a multicast packet only to a required particular port can not be realized unless the multicast router supporting the particular protocol is combined with the communication control unit.
In the multicast-supporting LAN described above, there is a communication control unit which packages IGMP as a management protocol of a multicast group between a multicast router and host devices on its own, but a merit such that a LAN switch by nature realizes high speed data transfer by forwarding a data packet in a data linked layer may be lost.
When a particular protocol specific to a device is used, connectivity between makers or devices can not be ensured.
It is an object to provide, to solve the problems described above, a communication control unit which can realize
Fujitsu Limited
Winder Patrice
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